New Wireless Security Standard Has Old Problem?

eggboard writes "Wireless security expert Robert Moskowitz, who sits on IEEE and IETF committees on that subject, sent me a short paper on a glaring weakness in the Wi-Fi Protected Access (WPA) protocol that's replacing the weak and broken WEP system well discussed here at Slashdot. His paper, which I've posted here, proves definitively that while WPA itself remains robust and secure, the interface for choosing consumer passwords makes it simple to snarf a tiny bit of network traffic and perform an offline dictionary attack. For Slashdot readers, this probably seems trivial, but because Linksys, Apple, and others are letting users enter My Dog Has Fleas as their passphrase, WPA might be less secure for home users than WEP."

Comments

This is *Supposed* to be hard

[TechyImmigrant]

The idea here (I know, I was there when we voted it into the standard) is that the PBKDF2 is computationally significant.

Thus when you perform your offline dictionary attack, for each lookup in the dictionary, you must perform 4096 HMAC_SHA1s and this might take some time if you are looking up a large number of dictionary entries.

The basic conflict is the wide disparity between the power of processors in low end 802.11 transceivers and high end computers. The time to compute the 4096 HMAC-SHA1s is significant on say a slow ARM7TDMI and the 4096 value is a compromise to limit the delay in computing this. This delay affects the time from pressing return on the keyboard, to the time the PTK can be known and communications can begin.

However the attacker can apply his cluster of 3GHz PCs, or his FPGA HMAC_SHA1 parallel processor, or his supercomputer array, and make the speed of dictionary lookups relatively insignificant compared against the strength of the passwords being used.

The wise people asked for a much higher number than 4096. Some implementation types beat it down to 4096, and here we are..

Re:At least use WEP!

[WuphonsReach]

We don't use WEP on our wireless net at the office. Too often, the interaction between the card and the access-point doesn't work well if WEP is enabled (different vendors for the two products).

Instead, we've segregated all of the WAPs onto a dead-end network where the users have to VPN into our LAN through a border server. (Basically treating them as if they were outside the office and coming in from an external ISP.)

Works pretty well, other then having to remember to VPN into the network. The traffic ends up encrypted (inside of the VPN tunnel), so it's not possible to sniff passwords.